In industry, numerous materials, often in granular or pebble-like form, are conveyed over long distances and may be often raised to considerable heights on an upward surface of a moving endless conveyor belt. Such materials may be dry, e.g., cement, dry ore from a mine, or even small machine components such as nuts or washers. On the other hand, with equal frequency, conveyor belts are utilized to move wet or sticky substances or objects, e.g., wet ore, pulverized coal that has been stored outside and is wet due to rain, or cooked objects such as cookies or candy. A very frequent problem encountered in the use of conveyor belts with both dry and wet materials is that after most of the material is delivered to reach a delivery point and leaves the belt, usually over a rotating end cylinder as the belt commences its return trip, some of the transported material stays on or with the belt. With dry material, with electrostatic forces sometimes responsible for the holding on of finely divided material to an electrically insulating belt, the problem usually is not very serious. On the other hand, with wet or inherently sticky materials, considerable amounts of material may stick to the belt and, thereafter, due to incidental vibration and the like, fall off below the belt support system and over a time pose serious problems.
It has long been known that the application of one or more scraper blades forcibly contacting the belt surface as it commences its return trip after going over an end cylinder helps remove material that has not separated from the belt as and when it should have. Among the numerous devices that are known in the prior art, are the one disclosed in U.S. Pat. No. 4,269,301 to Gibbs which teaches the use of a plurality of resilient scraper blades acting in tandem but individually pressed to a common belt, U.S. Pat. No. 4,182,444 to Fisher which teaches the use of a heated blade for removing materials such as hot asphalt mix, and U.S. Pat. No. 4,189,046 to Ward, deceased et al which teaches, inter alia, the use of flexible leaf springs to carry the scraper member and the provision of a cavity within the scraper member and communicating with the fluid pressure circuit that generates the force between the scraper element and the belt to deactivate the system when the scraper element has worn through to the cavity. In these and other similar prior art references the teaching almost invariably relates to the use of compressed air, with or without a pump to provide the same air pressure, as the fluid utilized in a cylinder and piston assembly to actuate the scraper blade element into scraping contact with the moving belt.
Even those prior art references which mention the use of some fluid other than compressed air, such as Ward, deceased et al, point out that it would not be desirable to allow the leakage of even a very small quantity of "hydraulic fluid" during the operation of the apparatus to actuate the blade scraper element. Such hydraulic fluid often is used at pressures in the range 1200-1500 psi. Persons skilled in the art, particularly persons familiar with the hazards that are ever present in underground operations such as mining, tunneling and the like, are usually very sensitive to the fact that in such confined quarters, in locations from which escape is usually difficult, electrical discharges, the presence of flammable fluids under high pressure or even sudden releases of compressed gases can very easily lead to explosions. These, at the very least, are extremely hazardous to life and limb and may prove life threatening. This is especially true in the mining of certain materials, e.g., coal, where there is the ever present danger of flammable gases to which the addition of compressed air in the event of a leak from the system could significantly multiply the potential danger of a hazardous explosion.
A need, therefore, exists for apparatus and methods for providing an actuating force to a belt scraping mechanism without the use of compressed air (and in particular without the use of electrically powered pumps or compressors to pressurize such compressed air supplies) or hydraulic fluids which upon the sudden release of very high pressure may form a fine mist, vapor or otherwise flammable gases.